1. Field of the Invention
The invention relates to a device for use with stuffing machines for stuffing shirred tubular casings having a uniform diameter. It particularly relates to a device which is adapted for mounting on the stuffing horn of such machines for effecting deshirring and smoothing of the shirred tubular casing prior to stuffing.
2. The Prior Art
It is known to use shirred tubular casings of a synthetic, semi-synthetic or natural material for the packaging of food items such as, for example, meat, in the form of sausages. The shirred casings utilized for this purpose, also called "sticks" or "hollow rods" by those skilled in the art, are produced by shirring and compressing long tubes of casing in the direction of their longitudinal axis to approximately one to three percent of their original length. In order to fill the shirred casing with sausage composition or other food product, conventionally one end of the shirred casing is first closed, and then the shirred casing is normally fit onto the stufffing tube of a stuffing machine. A sausage mixture is then forced, under pressure, through the stuffing tube into the casing, by which the shirred casing is continuously deshirred. After a predetermined length of the casing has been filled, the filled sausage casing is subdivided into cylindrical sausages which are then tied off and closed.
For a number of reasons, it is desirable that the diameter of the sausages thus produced remains constant over their entire length. Optimum filling of the tubular casing requires that a uniform diameter, the size of which is dependent upon the particular casing, be maintained over the entire length of the casing. If the casing is overstuffed, it may burst, while an insufficiently filled sausage will have a wrinkled surface.
Several prior art devices have been developed for uniformly controlling the diameter of the tubular casing during filling with sausage mixtures or other food products. Thus, it is known to fit a calibrating means to the opening of the stuffing horn, which prestretches the casing to be filled by pressing against the inside wall thereof. The contact pressure creates frictional forces between the calibrating device and the inner wall of the casing, which acts to slow down withdrawal of the casing from the stuffing horn (U.S. Pat. No. 3,457,588). Suitable calibrating means which have heretofore been used in the prior art comprise, for example, resilient fingers disposed at the rim of the stuffing horn opening, which are produced by forming slits therein (U.S. Pat. No. 3,264,679). These fingers press against the internal wall of the casing and thus enlarge it. By drawing the casing over these fingers during the stuffing process, a frictional resistance is created which controls the draw-off speed of the casing from the stuffing horn. This device has the disadvantage, however, that the frictional resistance is very high during the stuffing process, and the casing may thus tear. Furthermore, there is the danger of damage to the casing by the spread fingers. Moreover, the device does not represent an independent functional unit comprising a calibrating member and a tubular casing.
It has also been proposed to prepackage the shirred tubular casing together with a calibrating disk and to attach this combination to the stuffing horn prior to the filling operation (U.S. Pat. No. 4,007,761). The calibrating disk is disposed within an unshirred section of the casing and has an external circumference which must be larger than the internal circumference of the unshirred casing. During filling, the casing is drawn over the calibrating disk and is thereby stretched. The calibrating disk must therefore be made of a rigid, inelastic material in order to prevent its diameter from being altered by the pressure of the casing against the circumference of the calibrating disk.
This inelastic calibrating disk therefore has the disadvantage that in the case of fluctuations in the circumference of the casing--which cannot be entirely avoided during manufacture--an optimum filling of the casing is not achieved. When the internal diameter of the casing is too small, there is also the danger that it will be damaged or torn by the calibrating disk. At the very least, an undesirably high friction will occur between the casing and the calibrating disk, leading to overstuffing of the casing with sausage mixture and the inability to withstand the high pressures formed during boiling of the sausage.
A calibrating device is further known (U.S. Pat. No. 4,202,075) which is made of a flexible material and which has a variable diameter. This device is also intended to stretch and expand the tubular casing prior to its being filled with a sausage composition, while the device provides a controllable degree of expansion. Even with this device, however, strong frictional forces between the tubular casing and the calibrating device can occur.
Other prior art casing calibrating devices and stuffing arrangements are shown, for example, in U.S. Pat. Nos. 4,077,090, 4,017,941, and 4,034,441. Each of these arrangements employs a sizing disk having an external diameter somewhat larger than the internal diameter of the deshirred casing.